Since infection with the virus causing Acquired Immunodeficiency Syndrome (AIDS), HIV, as detected by the presence of specific antibodies to that virus, occurs in an increasing number of individuals who continue to have no or only very preliminary symptoms of actual clinical manifestations of the infection for prolonged periods, immunogenetic factors may contribute to the ability of different individuals to control virus effects. Many such individuals are being monitored in Houston for the possible development of clinical symptoms and signs and some are being treated in experimental protocols designed to evaluate whether or not certain antiviral agents may prevent the development of clinical symptoms and signs and some are being treated in experimental protocols designed to evaluate whether or not certain antiviral agents may prevent the development of clinical signs and/or increase T4 cell counts. Various studies indicate that some of these antibody positive individuals will develop clinical manifestations of the immunodeficiency syndrome each year. They also suggest that genetic and immunological parameters that may predict which clinical manifestations (i.e., Kaposi's sarcoma vs opportunistic infections) they might develop include histocompatibility type, complement allotype, cell surface phenotype profile, and in vitro immune function responses. The specific purpose of this project will be to collect histocompatibility, complement allotype, cell surface phenotype and immune function data for a large group of individuals with antibodies to HIV and to correlate these genetic/immune response factors to clinical course including responses to various prophylatic drug treatment protocols. Patients at all stages of possible responses to infection will be recruited as long as information is available as to the approximate likely data of initial infection or first appearance of antibody. Approximately 150 patients per year will be recruited for the study. Cell surface phenotype, including percentage of cells with T4 and T8 and dual staining T8-Leu 7, T8-T10, and T8-Dr, and relative immune responses to PHA, con A, pokeweed mitogen and allogeneic cells, will be assessed at least 3 times per year for each patient. Data from clinical studies relating to skin test responses will also be incorporated into the analyses.